According to the Volkskrant, the company ChickFriend, which is seen as the source of the fipronil scandal in the Netherlands, treated some poultry farms for blood lice in June last year already. The NVWA acknowledged that there may have been fipronil containing eggs in Dutch stores as much as a year ago. "We can not check that anymore, because those eggs are already eaten", a spokesperson said to the newspaper.

ChickFriend used a pesticide it got from a Belgian supplier, which added fipronil to it. It is now being investigated whether the Barneveld company knew that the pesticide contained fipronil.

Fipronil is an insecticide used against lice, ticks and fleas. It is also used in flea collars for cats and dogs. The World Health Organization considers fipronil to be "moderately toxic" to humans. In large quantities it can damage the liver, kidneys and thyroid gland. The European regulations for the use of fipronil was adjusted on January 1st this year. Fipronil is now banned from being used in pesticides in high concentrations.

The NVWA list of fipronil containing eggs no consists of 28 company codes. Only eggs with the code X-NL-40155XX (the Xs represent numbers) contain enough fipronil to be dangerous to everyone. The others on the list are only dangerous to children. The NVWA advises consumers not to feed their kids eggs stamped with any of the codes on the list, and to completely throw away any eggs stamped with X-NL-40155XX. The full list can be seen here.